Nope. Qlik Sense can't display message boxes. I suppose you could write a test routine that creates a list of excel files, then tries to load the first record. That will either succeed or fail. If you set the ErrorMode variable to 0 first then you can test after each load if an error occurred and log the file name to a table. After the load you can display the records of this table to see which files failed to load. Something like this: